I'm so sorry I missed this post earlier.
My hair got thinner whilst I was taking metformin too. I believe it is a side effect. I also lost a whole patch of hair a the back though, so my doctor put all the hair loss down to stress. I would see your doctor about it.
Have you changed your diet a lot too? I ask this because Metformin doesn't usually reduce BG levels by very much, and yours have dropped dramatically. Your doctor may suggest taking you off the metformin now? Mine won't prescribe it for me anymore because my BG's are near normal.